1. Field of the Invention
The invention relates generally to a system and method using temperature tracking for controlled oscillators (COs), and more particularly, to a system and method using temperature tracking for COs, in which the temperature tracking uses at least one coarse tuning capacitor circuit including a plurality of selectable coarse tuning capacitors.
2. Description of the Related Art
Modern communication systems typically employ a CO (e.g., voltage CO (VCO) or digitally CO (DCO)), in conjunction with a phase locked loop (PLL), to tune to a desired channel frequency. When PLL is locked, slow and gradual temperature tracking is typically used to compensate for the changes in a fine-tuning range of a CO, due to temperature changes.
Conventional systems sometimes use one or more capacitor configurations to perform temperature tracking. One such capacitor configuration can include a fine tuning capacitor circuit and a coarse tuning capacitor circuit. However, a frequency range of the fine tuning capacitor circuit is not capable of covering a wide range of temperature variations. Moreover, the coarse tuning capacitor circuit cannot provide temperature tracking when the PLL is locked.
An extra temperature tracking variable capacitor, e.g., a varactor, can be used in conjunction with the fine tuning capacitor circuit and coarse tuning capacitor circuit to further compensate for temperature variations. However, such types of capacitors tend to increase CO gain (KCO), which, in turn, can cause an increase in phase noise contribution due to the temperature tracking. In addition, varactors also tend to add parasitic capacitance to the output of the CO.
Therefore, there exists a need for a system and method using temperature tracking for COs, in which the temperature tracking uses at least one coarse tuning capacitor circuit including a plurality of selectable coarse tuning capacitors.